{
  "abstract": "Underground coal gasification (UCG) is an important in situ conversion technology for the clean and efficient recovery of deep and difficult-to-mine coal resources. Reactions between high-temperature char and gasifying agents such as CO2 and H2O in the reduction zone directly control the generation of valuable gases, particularly CO and H2. Calcium-bearing minerals can catalyze char gasification and participate in high-temperature ash-phase transformation. However, the differential effects of CaCO3 and CaO on coal pyrolysis–gasification behavior and ash-phase evolution under a CO2 atmosphere remain unclear. In this study, a typical low-rank Jiangna (JN) coal from the Hami region of Xinjiang, China, was subjected to sequential HCl-HF leaching to prepare demineralized coal (DC), which was subsequently loaded with 5 or 10 wt% CaCO3 or CaO. TG-FTIR-MS, high-temperature in situ XRD, SEM, N2/CO2 adsorption, and multifractal analysis were employed to investigate thermal conversion, gaseous product release, pore structure, and Ca-bearing phase evolution. Demineralization decreased the mass loss at 600–1000 °C from 50.05% to 29.14%. The CaCO3-loaded samples showed their main high-temperature mass-loss and FTIR CO-band responses above 800 °C, whereas the CaO-loaded samples showed an earlier apparent high-temperature mass-loss response at 600–800 °C. At 600 °C, the CaO-loaded samples exhibited greater mesopore development. At 900 °C, the CaCO3-loaded samples exhibited pronounced micropore and mesopore development, with micropore volume increasing by 49.1–64.9%. The nonlinear mass scaling function τ(q) and the decrease in the generalized dimension D(q) with increasing q indicated heterogeneous multiscale distributions of pore volume. At 600 °C, the micropore spectrum width (Δα) of the CaCO3-loaded samples was 0.5537–0.6375, higher than that of the CaO-loaded samples (0.4093–0.4198). In contrast, the mesopore Δα of the CaO-loaded samples was 0.6688–0.9901, markedly higher than that of the CaCO3-loaded samples (0.1660–0.2126). At 900 °C, the CaCO3 and CaO-loaded samples exhibited contrasting micropore and mesopore multifractal responses. The CaO-loaded samples showed an earlier apparent high-temperature mass-loss response under the tested conditions. However, equal-mass additive loading prevented separation of the effects of precursor form and Ca input. Although HT-XRD detected crystalline phase changes, the active Ca species and extent of Ca incorporation into ash phases remain unresolved. These results document different temperature-dependent responses to CaCO3 and CaO addition under the tested conditions. These findings provide an experimental basis for selecting Ca-based additives, regulating valuable gas generation, and evaluating high-temperature ash stability in UCG.",
  "abstract_shown": true,
  "affiliations": [
    "School of Geology and Mining Engineering, Xinjiang University, Ürümqi 830017, China",
    "Inner Mongolia Research Institute, China University of Geosciences, Ordos 017010, China",
    "School of Earth Resources, China University of Geosciences, Wuhan 430074, China",
    "Xinjiang Academy of Geological Research, Ürümqi 830099, China"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 7,
  "authors": [
    {
      "affs": [
        0,
        1
      ],
      "name": "Yufei Zhang"
    },
    {
      "affs": [
        1,
        2
      ],
      "name": "Jijun Tian"
    },
    {
      "affs": [
        3
      ],
      "name": "Shuguang Yang"
    },
    {
      "affs": [
        0
      ],
      "name": "Shuo Feng",
      "orcid": "0009-0008-4775-1844"
    },
    {
      "affs": [
        2
      ],
      "name": "Daxing Wang"
    },
    {
      "affs": [
        0
      ],
      "name": "Xin Tong"
    },
    {
      "affs": [
        2
      ],
      "name": "Chengjie Xu"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/cmc42mqk6bsxy.bib",
  "cited_by": 0,
  "doi": "10.3390/fractalfract10100722",
  "fulltext_url": null,
  "id": "cmc42mqk6bsxy",
  "issns": [
    "2504-3110"
  ],
  "landing_url": "https://www.mdpi.com/2504-3110/10/10/722",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2210|Mining and Gasification Technologies"
    ]
  ],
  "openalex": "W7222130332",
  "pdf_url": null,
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-15",
  "publisher": "MDPI AG",
  "ris": "https://research.draconitic.com/paper/cmc42mqk6bsxy.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:32Z",
      "native_id": "10.3390/fractalfract10100722",
      "source": "crossref",
      "url": "https://www.mdpi.com/2504-3110/10/10/722"
    }
  ],
  "subjects": [
    {
      "field": "mathematics",
      "origin": "issn:2504-3110",
      "subfield": "analysis-pdes"
    }
  ],
  "title": "Effects of CaCO3 and CaO Loading on Pore Structure, Multifractal Evolution, and Product Transformation During CO2 Gasification of Low-Rank Coal",
  "title_text": "Effects of CaCO3 and CaO Loading on Pore Structure, Multifractal Evolution, and Product Transformation During CO2 Gasification of Low-Rank Coal",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:32Z",
  "url": "https://research.draconitic.com/paper/cmc42mqk6bsxy",
  "venue": "Fractal and Fractional",
  "versions": []
}